1. Technical Field
The present invention relates to a rotary angle detecting device applied to a rudder angle sensor or the like for a vehicle, and more particularly, to a rotary angle detecting device in which a synthetic-resin wheel member provided with a detecting portion is attached to a steering shaft to rotate together.
2. Related Art
A technique is known in which a rotary angle detecting device is disposed between a vehicle body and a steering shaft of a vehicle, and a deceleration force control of a suspension, a shift position control of an automatic transmission, or a rear-wheel steering control of a four-wheel steering vehicle is carried out on the basis of a steering angle, a steering speed, etc. of a steering wheel detected by the rotary angle detecting device.
In general, in many cases, this kind of rotary angle detecting device includes a rotatable wheel member having a detecting portion such as a code pattern row, a circuit board mounted with a signal detecting element and the like, and a housing (case and cover) accommodating the wheel member and the circuit board and attached to a vehicle body side, wherein the wheel member is attached to the vicinity of the front end portion of a steering shaft so that the wheel member rotates together with the steering shaft upon turning the steering wheel (for example, see U.S. Pat. No. 7,091,474 which corresponds to Japanese Unexamined Patent Publication No. 2006-17663, Pages. 5 to 8, FIG. 1). Likewise, when the wheel member is attached to the vicinity of the steering shaft, it is possible to detect rotary information (a rotary amount or a rotary direction) of the steering shaft in such a manner that a signal detecting element such as a photointerruptor detects a position variation of the code pattern row or the like accompanied by the rotation of the wheel member.
In the rotary angle detecting device in which the wheel member (wheel member 4) having the detecting portion is attached to the steering shaft having a pair of flat surfaces provided in the front end portion thereof, it is necessary to carry out an operation in which a central opening of a cylindrical portion (wheel portion 52) of the wheel member is directly or indirectly fitted to the outside of the front end portion of the steering shaft via an appropriate member. Additionally, it is necessary to hold the wheel member attached to the steering shaft in terms of the attachment operation so as not to be slid or rattled in a rotary direction. For this reason, in the past, the wheel member is press-inserted in an axial direction of the steering shaft to be directly or indirectly strongly fitted thereto during the attachment operation in order for the attached wheel member not to slide or rattle with respect to the steering shaft in a rotary direction. However, since it is necessary to apply a comparatively large press-inserting force to the wheel member during the attachment operation, a problem arises in that workability is very poor.
Additionally, it may be supposed that the strength of the wheel-member-side fitting against the steering shaft is made to be slightly weaker in order to improve the workability of the attachment operation of the wheel member. However, when the wheel-member-side fitting strength is made to be weaker with a general structure, the attached wheel member slides or rattles with respect to the steering shaft in a rotary direction, thereby causing a problem in that it is difficult to obtain satisfactory detection precision.